Hey guys, I have another stumper. 2000 Buick LeSabre 3800 surges when warm.

Not nearly as foolish as I would have felt if I had been able to check it and didn't. I'm going to get a tester on the way home tonight and see what it is.

 

Good to test that and get it out of the way. We replace alot of fuel pumps at this Chevy dealership. But usually they are not running when they get here. I work beside the running problem guy and he hooks up the fuel gauge on alot of cars that run funny.

 

Jim, clarifications in brackets added. Also with engine idling, you should see a jump in pressure of 7-10 psi when vacuum hose on regulator is removed. You will need the specs for your particular model.

 

I just looked up those codes and the 420 is set if the o2 sensor after the converter switches to fast compared to the ist one. The second one should change slower because of the converter doing it's job. You may have a converter getting clogged. P0422 don't exist on that car. P1133 says that #1 o2 sensor doesn't switch from rich to lean and lean to rich enough. That might be a sensor but if the car stays running to lean then it wouldn't be switching enough.

 

Got a fuel pressure tester from AZ. 44 when I start it, then it levels off at 40 and stays rock solid. It ran for several minutes without skipping a beat, then started surging and died when it was fully warmed up. I also grabbed a coolant temp sensor while I was there and will try that in a little while. Even with the surging the pressure stayed at 40.

 

Coolant temp sensor didn't make a difference either. I guess all I can do now is wait until I get the scanner and see what all that shows.

 

I was just looking at what GM said about 48-55 with key on pump running. So you would have to watch the gauge when you turned the key on and the pump would for 5 seconds and read it during that time. When it quits running it shouldn't drop 5-10 pounds. So if its at 40 it's too low. take the regulator hose off and see what it reads then. It should go up about 10lbs I would think.

 

Tested it again, solid 40 and it goes up to 50 when I pull the vacuum line off. Put the line back on and it drops to 40. As soon as it gets to normal temp it chugs and dies but the pressure doesn't drop at all. Again, it runs fine until then. I would think if the converter was plugged it would do it much sooner because it takes several minutes to get from cold to normal running temp.

I checked the vacuum hoses again and found one that was cracked. It is a U-shaped hose on the front of the valve cover with plastic lines running to and from it. I swiped it off my other car and it still does the same thing. This one isn't mine by the way, it's a picture I found online. The crack was very hard to see but I found it by spraying carb cleaner on it.

 

Have you went back to the tail pipe and see if it don't have much pressure coming out? and is you hold your rpms up about 2000 you might hear a sound like exaust is trying to force its way out somewhere. Larry said put the vacuum gauge on it and hold the rpms to 1500 and see if the vacuum drops off.

 

Can't find my vacuum gauge but I did check the tailpipe and it seems normal.

 

You said you replaced the ignition module. Was that lifetime warranty?

 

I have not changed the ignition module but I did pick up a new fuel filter. I haven't put one on in the 120,000 I've been driving it. But again, why only when it gets warmed up and not at the beginning?

 

You have not replaced the fuel filter in 120k miles??? Man you will be lucky if the fuel pump doesnt crap out after you replace that. I have seen many times where cars had a running issue to find the filter was OEM and never replaced. Replace the filter and drive issue clears up, week or two later fuel pump quits and the dealer would get blamed for it.

 

Well this is going to be fun... my son's Malibu filter is above the rear axle where it was easy to get to and not rusty. Mine is along the driver's side frame rail and the screw end is rusty as ****. Wish me luck.

 

Wire brush the threads, lube them and one trick i always used was take a air hammer with a blunt tip and burp it around the "nut" of the filter to loosen the rust, then carefully try to loosen the line nut. Does this filter have the nipple on one end and nut on the other or the nuts on both ends? If it has the nipple take it off and just try to thread the filter off with out turning the line nut so you do not twist the line.

 

Yep, it twisted off. I got a repair kit for the line, got the fuel filter on, no leaks, it starts up but now it won't idle at all. I can keep it going if the RPMs are above 2000 but it won't idle once I let off. It doesn't surge at those RPMs now so I have a different problem and still no codes. I don't have the fuel pressure gauge now and can't find the damned hose for my vacuum gauge. I feel like I'm running in circles again.

---------- Post added at 06:24 PM ---------- Previous post was at 05:30 PM ----------

Well ok, I feel really stupid but I realize I hadn't actually swapped the MAF sensor with the one off my other car, I cleaned the original with MAF cleaner. So I took it off the other car and it ran for 15 minutes without a hitch.

Hm.

So did I actually have two separate problems? A fuel filter AND the MAF? Why didn't the MAF throw a code? I'm going to drive it later and see how it acts on the road but 15 minutes in the garage should have been a good indicator. While it was running I took some readings with this new tool I got online.

Fuel 1 - (was open earlier) Closed
Fuel 2 - N/A
Calculated Engine Load - 3%
Engine coolant temp - 208
Short term fuel trim - ranged between -3.1 to -4.7
Long term fuel trim - -25.0
Intake manifold absolute pressure - 8.6
Engine RPM - 925
Timing advance #1 - 25.0
Air Intake Temp - 90

Then it disconnected and wouldn't re-connect (bluetooth) and I didn't get the rest of the readings.